With the advent of information era, conventional cathode ray tube (CRT) displays are being replaced by flat panel displays. Currently, one of the most widely used flat panel displays is liquid crystal displays (LCDs). LCDs have the characteristics of low power consumption and light weight, however, due to the LCDs are not self-luminous, there are technical limitations in terms of contrast, viewing angle and area and size. The organic light emitting diodes (OLEDs) have the characteristics of self-luminous, wide viewing angle, short response time, high luminous efficiency, wide color gamut, low operation voltage, thin panel, and can be used for making large-size and bendable displays so that much attention has been paid thereto.
The existing OLED display device (as shown in FIG. 1) mainly comprises a substrate, and a light emitting unit formed on the substrate which is composed of a transparent anode 7, a cathode 1 composed of alloys and a series of organic thin layers sandwiched between the anode 7 and the cathode 1, the organic thin layer is generally divided according to the function and generally comprises a hole injection layer (HIL) 6, a hole transport layer (HTL) 5, an electron transport layer (ETL) 3, and an electron injection layer (EIL) 2 in sequence from the anode side. Some devices further include a hole blocking layer (HBL) and an electron blocking layer (EBL) as required.
Since the electron transport rate of most organic materials is much smaller than the hole transport rate, it has been one of the main topic of research in the industry to find an ETL whose electron mobility is comparable with the hole mobility of a HTM and which can improve its efficiency and reduce the voltage, with other conditions being satisfied.